Image annotation refers to a process in which specific areas of an image are marked by adding text, color overlays, etc. In particular, graphical annotations such as curves, lines, symbols, etc., henceforth referred to as markers, may be added. It is known to annotate images by hand, e.g., using a pen or a pencil. Moreover, it is known to use a system to annotate images in an interactive manner. In such a system, the user may operate a user interface device such as a mouse to draw or drag markers on a displayed image, and in response, the system draws or places the markers accordingly on the displayed image.
US 2007/0174769 A1 describes a system and a method for enhancing the delivery and display of medical images for preoperative planning and diagnosis. It is said that a user may select an initial annotation, operate the system to modify the initial annotation along the displayed image in association with anatomical features, and then fix the appropriate annotation at the desired location on the displayed image for later reference.
Moreover, in reference to labeling vertebrae, it is disclosed that the system may be used to automatically label vertebrae. Specifically, a user may select an initial annotation and associate it with a vertebra. Once this is done, the system will automatically label the remaining vertebrae extending superiorly and inferiorly from the initial reference vertebrae as they were previously mapped by the machine reader.
A problem of the above system is that it is inconvenient for the user to accurately place an annotation at a desired location in the displayed image.